radioreceptor assay

noun

ra·​dio·​re·​cep·​tor assay -ri-ˈsep-tər- 

: an assay for a substance and especially a hormone in which a mixture of the test sample and a known amount of the radiolabeled substance under test is exposed to a measured quantity of receptors for the substance and the amount in the test sample is determined from the proportion of receptors occupied by radiolabeled molecules of the substance under the assumption that labeled and unlabeled molecules bind to the receptor sites at random